The overall objective is to gain insight nto the mechanism of protein accretion in early postnatal life: specifically, to assess how nutrient intake may increase protein synthesis and/or restrain proteolysis, and to examine how these processes may be affected by the stage of development. In contrast to the continuous substrate delivery of the intrauterine environment, the newborn must rapidly adapt to intermittent and varying nutrient intakes. To compensate for periods of fasting when mobilization of endogenous stores is necessary, the newborn must efficiently accumulate substrate during periods of feeding. The capacity to adequately utilize, conserve, and accumulate protein provided intermittently is fundamental to normal growth and development. Therefore, an examination of the mechanisms of protein accretion is critical to understanding normal and abnormal growth.